1. Field of Invention
The invention generally relates to methods and apparatuses for transporting diverse traffic types such as different types of layer-2 traffic over an optical transport network such as a SONET/SDH network. The invention more particularly relates to utilizing pseudo-wires carried directly on top of the SONET, SDH, or OTN layer to transport diverse data packet traffic types such as various types of layer-2 traffic.
2. Description of Related Art
Service provider communication networks today consist of multiple types of equipment designed to transmit and route many kinds of traffic. Traditionally, these networks evolved from voice/telephone service so they were designed to carry fixed-sized circuit connections between end users. As data applications have evolved and capacity requirements have grown, several generations of packet switched networking equipment was installed into networks to route the packet data. Examples include ATM, Gigabit Ethernet, and MPLS, as shown in FIG. 21.
While new packet switching technologies continue to emerge, service providers must continue to service older technologies as it takes many years for end users to phase out a particular technology. This has led to the service providers maintaining several independent packet switched networks to carry the different types of service. Provisioning and maintaining these multiple networks is costly and it would be advantageous to converge these packet switched networks onto a common network. As shown in FIG. 21, Layer-2 and MPLS switches are deployed to aggregate data flows into SONET backbone.
Conventionally circuit switched connections are used to provide transport functions between the various packet switching network equipment. But these circuit switched connections are limited in flexibility: they are available in limited bandwidth sizes: 10 Gbps, 2.5 Gbps, 622 Mbps, 155 Mbps, 53 Mbps, 1.5 Mbps, 64 Kbps, and are provisioned and maintained independently of the packet switched traffic. The static nature of these circuit connections imposes inefficiency in utilization of the capacity of the circuit switched network when carrying packet data traffic.
As a result, the interface between the packet data layer (layer 2) of the carrier network and the circuit switch layer (layer 1) leads to network utilization inefficiencies and difficult and expensive provisioning and maintenance tasks for the service providers.
The invention described herein presents a method to couple the Layer-2/MPLS packet data convergence function directly onto circuit switch equipment and integrate the control and management of connections in layer 1 and 2. Integration of these functions will greatly reduce provisioning and maintenance expenses of carrier networks and improve the utilization of the network capacity. The benefit of the invention is evident in FIG. 22.
Luca Martini and others have introduced the concept of pseudo-wires in a number of Internet Engineering Task Force (IETF) drafts, which has been widely referred to as “draft-martini”. In Martini's design, some pseudo-wires can be initiated from the edge of multi-protocol label switching (MPLS) and/or IP backbone networks. Once established, a customer's layer-2 traffic can be aggregated into the pseudo-wires. To control the pseudo-wires, LDP (label distribution protocol) messages are routed through the backbone network to communicate between network edges. A serious drawback with the draft-martini design is that communication carriers must rely on MPLS/IP backbones with expensive high-performance routers to support the control messaging and label distribution protocol thereby greatly increasing the cost of transporting Layer-2 traffic which is otherwise inexpensive and relatively simple. In reality, these routers are essentially used to perform relatively trivial switching functionality.
In a parallel development, the Optical Internetworking Forum (OIF) has defined a user-network interface (UNI) specification that allows users to request the creation of Synchronous Optical Network (SONET) connections for data traffic. However, there are a number of issues in the UNI approach:                Both user and network elements must implement the UNI specification thereby dramatically increasing the cost of implementation and creating compatibility problems with non-UNI networks that interface with the UNI-enabled network.        The existing OIF UNI is only designed to interface user and network elements over optical interfaces.        
George Swallow and others have proposed an overlay model where MPLS routers can use an RSVP (resource reservation protocol extension for traffic engineering) protocol to communicate with a GMPLS-enabled (generalized multi-protocol label switching-enabled) optical backbone. This approach can potentially introduce user traffic aggregation from optical network edges. However, this model requires MPLS and IP to be used across the transport networks. Also, this approach may require the carriers to reveal internal routing and resource information to the external customers, which is not practical in most of the operational networks today.
There have been a number of advancements of SONET/SDH technology in recent years. For example, Virtual Concatenation provides the flexibility that allows edge switches to create SONET/SDH connections with finer granularity bandwidth. Link Capacity Adjustment Scheme (LCAS) uses several control bits in the SONET/SDH frame to increase or decrease a connection's bandwidth. Finally, Generic Framing Procedure (GFP) specifies the framing format for a number of link protocols, such as Ethernet and PPP.
It is admitted that MPLS, LDP, draft-martini, and OIF UNI, Virtual Concatenation, LCAS and GFP are conventional elements with respect to the invention. Although the invention utilizes some of these conventional elements, details of which may be found in available literature, the methods and apparatuses disclosed and claimed herein differ substantially therefrom. In other words, the invention leverages such conventional technologies in unique ways to achieve a method and apparatus for transporting packet data from customer data nodes over an optical network.